250GB startup disk full in 3 months?

Hello and sorry, I know there are many threads about this topic but after doing some research I couldn't find any suitable for my problem.

So, I have 3-months-old Air with double memory 250 MB which keeps telling me the startup disk is full. Programs don't run anymore and I can't save any material, which makes my life difficult since all my life goes through this laptop

I don't download music nor movies. Only thing that could take the storage are pictures, but when I go to see the storage to "About this Mac" it says that all the storage is taken by the category "other".

My desktop Mail ahsnt worked for a while, can it have something to do with this? It really feels that there is something weird, a file duplicating itself or something. Because I keep removing more and more files and it just gets fuller.

I really pray for someone to help me, I can't operate anything anymore

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